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LSF_ROTATE

LSF_ROTATE:

Purpose

Create a 1-d convolution kernel to broaden a spectrum from a rotating star

Explanation

Can be used to derive the broadening effect (line spread function; LSF)
due to rotation on a synthetic stellar spectrum. Assumes constant
limb darkening across the disk.

Calling Sequence

lsf = LSF_ROTATE(deltav, vsini, EPSILON=, VELGRID=)

Input Parameters

deltaV - numeric scalar giving the step increment (in km/s) in the output
rotation kernel.
Vsini - the rotational velocity projected along the line of sight (km/s)

Output Parameters

LSF - The convolution kernel vector for the specified rotational velocity.
The number of points in LSF will be always be odd (the kernel is
symmetric) and equal to either ceil(2*Vsini/deltav) or
ceil(2*Vsini/deltav) +1 (whichever number is odd). LSF will
always be of type FLOAT.
To actually compute the broadening. the spectrum should be convolved
with the rotational LSF.

Optional Input Parameters

Epsilon - numeric scalar giving the limb-darkening coefficient,
default = 0.6 which is typical for photospheric lines. The
specific intensity I at any angle theta from the specific intensity
Icen at the center of the disk is given by:

I = Icen*(1-epsilon*(1-cos(theta))

Optional Output Parameter

Velgrid - Vector with the same number of elements as LSF

Example

(1) Plot the LSF for a star rotating at 90 km/s in both velocity space and
for a central wavelength of 4300 A. Compute the LSF every 3 km/s
IDL> lsf = lsf_rotate(3,90,velgrid=vel) ;LSF will contain 61 pts
IDL> plot,vel,lsf ;Plot the LSF in velocity space
IDL> wgrid = 4300*(1+vel/3e5) ;Speed of light = 3e5 km/s
IDL> oplot,wgrid,lsf ;Plot in wavelength space

Notes

Adapted from rotin3.f in the SYNSPEC software of Hubeny & Lanz
.http://nova.astro.umd.edu/index.html Also see Eq. 17.12 in
"The Observation and Analysis of Stellar Photospheres" by D. Gray (1992)

Revision History

Written, W. Landsman November 2001

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